Transcontinental pollution: This graphic shows particulate pollution in the atmosphere, particularly being transported from East Asia across the North Pacific in May 2003, as observed by the moderate resolution imaging spectroradiometer (MODIS) onboard the Terra satellite. Particulate pollution is represented by optical thickness, in which heavy aerosol concentrations appear in shades of brown, with darker shades representing greater concentrations.
The instrument also gets “spatial and time detail that one would never get from ground-based measurements, and it captures the entire pollution plumes rather than just having a few observing stations looking up,” says Prinn.
NASA researchers drew two virtual lines at 20 degrees north to 60 degrees north, and they measured the optical effect of the particles as they crossed those lines, says Yu. Using software that he made, the researchers culled this data and mapped it to see globally where the pollution is located.
The researchers found that 18 teragrams–almost 40 billion pounds–of pollution is exported from Asia, and that 4.5 teragrams–10 billion pounds, or about 25 percent–reaches North America annually, says Mian Chin, an atmospheric scientist at NASA and a coauthor of the study. But the instrument measures the total atmosphere column and does not have the vertical structure, so it is unknown how many of the pollutants are at surface level, and how many are aloft in the atmosphere, says Chin.
Despite that uncertainty, the scientists say that it is the higher-altitude pollution that is probably most worrisome. “We think the pollution being imported to North America will impact the weather and climate; we don’t expect any big impact on the air quality because particles from East Asia are exported at high altitude,” says Yu.
“It is very difficult to lower pollution levels of man-made pollutants to extremely low levels because pollutants come in the air from other countries that the U.S. Environmental Protection Agency, for example, cannot control,” says Prinn. Agrees Honrath: “You have to consider the future industrial growth of Asia if you develop long-range plans for meeting air-quality goals in the United States.”